Hydroacoustic Research Articles

Environmental DNA and Hydroacoustic Surveys for Monitoring the Spread of the Invasive European Catfish (Silurus glanis Linnaeus, 1758) in the Guadalquivir River Basin, Spain.

The European catfish (Silurus glanis Linnaeus, 1758) was introduced into the Ebro Basin in Spain in 1974 for recreational fishing. Since then, the species has spread throughout the country's river basins, reaching the Iznájar Reservoir (Guadalquivir River Basin) in 2011. This area is of great ecological and economic relevance, especially as it includes the Doñana National Park, one of the most important nature reserves in Europe. Recently, the presence of catfish has been reported in the lower reaches of the river. In this work, we used non-invasive vertical and horizontal hydroacoustic surveys and environmental DNA river sampling to unravel the actual distribution and dispersal pattern of the species in the lower Guadalquivir River. The hydroacoustic profiles and the species-specific detections by real-time PCR (qPCR) and droplet digital PCR (ddPCR) showed that these non-invasive methods allow the detection and quantification of catfish and provide valuable information on the species' presence. We have confirmed the presence of catfish in most of the study area, including downstream areas of the Guadalquivir Basin. The results suggest the possibility of other isolated introductions and/or human-mediated movements of specimens, and imply that a coordinated catfish prevention and mitigation strategy is therefore urgently needed.

Aerial drones and recreational fish finders: evaluating a low-cost method for surveying fish aggregations

Context Globally, anthropogenic activities such as fishing and industrial development have affected fish abundance. Cockburn Sound, a crucial spawning site for the sparid Chrysophrys auratus near Perth, Western Australia, faces potential impacts from ongoing infrastructure development, such as ports. Aims To inform environmental-impact assessment, innovative non-extractive methodologies are needed to quantify C. auratus aggregation abundance. Methods This study evaluated an ‘aerial–acoustic survey method’ that combines data from aerial drones and recreational fish finders. We investigated the ability of both methods to identify C. auratus aggregations across known spawning sites, types of proxies of abundance obtained, the practicality of each method in ambient environmental conditions and survey costs. Key results By integrating drones and fish finders, surface and subsurface aggregations of C. auratus were documented over two spawning periods (September–November in 2022 and 2023), capturing important parameters related to aggregation frequency, distribution and size. Conclusions Although initial equipment investments were modest, expenses for survey planning, operations and data analysis were substantial. Nevertheless, this approach offers a cost-effective alternative to using more expensive scientific-grade equipment. Implications The study presents a promising methodology for assessing distribution and abundance as part of environmental impacts in infrastructure developments and managing resources, in ecologically sensitive areas such as Cockburn Sound.

Ecosystem [512]: Acoustic Ecology Surveys as Music

Acoustic ecology is a rapidly expanding discipline which can reveal details about ecosystems that are not visually apparent, and field recording has been used in an increasing variety of ways in music compositions, opening the door to collaborative projects that walk the line between science and art. Ecosystem [512] is rooted in acoustic surveys that I carried out over nine months in Iceland’s National Parks. These surveys provided more than 10,000 hours of recordings that are processed, compressed, combined, and analyzed before being used as the fundamental material for a music composition for electronics and clarinet. The piece uses multiple strategies such as algorithmic composition to handle the transition from rough acoustic survey recordings to final music product. The process of composing this piece reveal insights about both acoustic ecology processes and music composition considerations.

Fish Distribution in Lacustrine and Riverine Biotopes of Bratsk Reservoir Based on the Results of Hydroacoustic Surveys

Abstract Fish distribution in different areas of Bratsk Reservoir has been studied using hydroacoustic equipment. The average abundance of fish decreases (r = –0.70; p < 0.05; R 2 = 0.49) from the near-dam reach (214 ± 34 ind./ha) to the water area in the upper reaches of the reservoir (113 ± 43 ind./ha). A similar relationship is observed in the dynamics of the abundance of early juveniles and the immature fish population. However, such relationship has not been found in fish with a size of more than >100 mm, which with a low abundance are relatively evenly distributed along the longitudinal axis of the reservoir (10.5 ± 6.6 ind./ha). The common perch (Perca fluviatilis Linnaeus, 1758) is the most abundant species in the reservoir, its highest concentrations are recorded in the lower lacustrine part of the reservoir (139 ± 22 ind./ha). Less abundant cyprinids (Cyprinidae) (41 ± 15 ind./ha) and whitefishes (Salmonidae, Coregoninae) (12 ± 4 ind./ha) are more evenly distributed along the longitudinal axis of the reservoir. Temperature stratification of the water column is an important factor in the ecological differentiation of the fish population in the reservoir. The major part of the ichthyomass consisting of relatively warm-water fish species from the families Percidae and Cyprinidae (common roach (Rutilus rutilus (Linnaeus, 1758) and common bream (Abramis brama (Linnaeus, 1758)) is concentrated in the warming up epilimnion. The fish population in the cold hypolimnion consists of single individuals of the Baikal omul (Coregonus autumnalis (Georgi, 1775)) and peled (C. peled (Gmelin, 1789)). Transverse distribution of fish depends on the presence of a runoff flow. At relatively high flow rates, fish begin to avoid the midstream part in the studied sites of the reservoir and concentrate in the floodplain areas (R 2 = 0.54; p < 0.0001).

Temporal and Spatial Distribution Characteristics of Fish Resources in a Typical River–Lake Confluence Ecosystem During the Initial Period of Fishing Ban

This study provides a comprehensive analysis of the spatio-temporal dynamics of fish resources in the confluence waters of Poyang Lake and the Yangtze River, focusing on the initial phase of a 10-year fishing ban implemented in January 2020. Through hydroacoustic surveys conducted during both high-water (September 2020) and low-water (January 2021) periods, we identified significant variations in fish density and individual size across different sections. During the high water level period, fish concentrations were primarily observed in the confluence area between the Yangtze River and Poyang Lake, exhibiting higher densities compared to other regions. Conversely, fish congregated in the deep-water zones of the main river during the low water level period. The fish population was dominated by small to medium-sized individuals, with mean body lengths of 12.47 cm and 12.62 cm during the high and low water level periods, respectively. Notably, 42 and 33 fish species were recorded during the high-water and low-water surveys, respectively, emphasizing the region’s rich biodiversity. Importantly, the study demonstrates that the fishing ban has resulted in substantial increases in both fish density and mean body length, underscoring its effectiveness in fostering fish population recovery. These findings provide critical baseline data to inform scientific conservation and management strategies in this ecologically sensitive river–lake ecosystem.

Self-supervised feature learning for acoustic data analysis

Acoustic surveys play a pivotal role in fisheries management. During the surveys, acoustic signals are sent into the water and the strength of the reflection, so-called backscatter, is recorded. The collected data are typically annotated manually, a process that is both labor-intensive and time-consuming, to support acoustic target classification (ATC). The primary objective of this study is to develop an annotation-free deep learning model that extracts acoustic features and improves the representation of acoustic data. For this purpose, we adopt a self-supervised method inspired by the Self DIstillation with NO Labels (DINO) model. Extracting useful acoustic features is an intricate task due to the inherent variability and complexity in biological targets, as well as environmental and technical factors influencing sound interactions. The proposed model is trained with three sampling methods: random sampling, which ignores class imbalance present in the acoustic survey data; class-balanced sampling, which ensures equal representation of known categories; and intensity-based sampling, which selects data to capture backscatter variations. The quality of extracted features is then evaluated and compared. We show that the extracted features lead to improvement, in comparison to using the untreated data, in the discriminative power of several machine learning methods (k-nearest neighbor (kNN), linear regression, multinomial logistic regression) for ATC. The improvement was measured through higher accuracy in kNN (77.55% vs. 71.93%), Macro AUC in logistic regression (0.92 vs. 0.80), and R2 in linear regression (0.69 vs. 0.45) when comparing extracted features to the untreated data. Our findings highlight the advantage of applying emerging self-supervised techniques in fisheries acoustics. This study thus contributes to the ongoing efforts to improve the efficiency of acoustic surveys in fisheries management.

Accuracy and Precision of Shallow-Water Photogrammetry from the Sea Surface

Mapping shallow-water bathymetry and morphology represents a technical challenge. In fact, acoustic surveys are limited by water depths reachable by boat, and airborne surveys have high costs. Photogrammetric approaches (either via drone or from the sea surface) have opened up the possibility to perform shallow-water surveys easily and at accessible costs. This work presents a simple, low-cost, and highly portable platform that allows gathering sequential photos and echosounder depth values of shallow-water sites (up to 5 m depth). The photos are then analysed in conjunction with photogrammetric techniques to obtain digital bathymetric models and orthomosaics of the seafloor. The workflow was tested on four repeated surveys of the same area in the Western Mediterranean and allowed obtaining digital bathymetric models with centimetric average accuracy and precision and root mean square errors within a few decimetres. The platform presented in this work can be employed to obtain first-order bathymetric products, enabling the contextual establishment of the depth accuracy of the final products.

Acoustic detection rate can outperform traditional survey approaches in estimating relative densities of breeding waders

Passive acoustic devices are increasingly being used to monitor biodiversity. However, few studies have compared the accuracy of acoustic surveys and traditional surveys against ground‐truthed data. Here, we assess whether acoustic recorders used in conjunction with an artificial intelligence (AI) classifier can predict the relative breeding density of four wader species better than traditional fieldworker transect surveys. In a 27‐km2 upland study site, acoustic data were collected at 83 sampling points and analysed using the BirdNet bird‐sound classifier to estimate vocal detection rate at each location; we also carried out concurrent transect bird surveys. To ground‐truth these approaches, intensive field surveys were undertaken to identify each breeding territory of our focal species. With both the acoustic dataset and the transect dataset, we used similar analytical approaches (random forest regression trees) to predict relative territory density across the study site, and then compared these predictions with the territory density obtained from the intensive field surveys. The classifier performed well at identifying the presence of target species' vocalizations within 3‐s periods for Lapwing (accuracy = 0.911), Curlew (0.826) and Oystercatcher (0.841), but less well for Golden Plover (0.699). For Curlew and Oystercatcher, the predictions obtained from the acoustic approach were a better fit to actual territory density than the transect approach. In contrast, for Lapwing and Golden Plover, the transect predictions outperformed the acoustic predictions, with the acoustic model particularly poor for Golden Plover. We attributed these differences to the performance of the classifier, species' ecology and vocal behaviour. Data gathering for the acoustic approach was more time‐efficient than the transect surveys, requiring less than a quarter of the fieldworker days. We conclude that there is high potential for acoustic approaches to augment traditional methods, although species' ecological characteristics should be considered: species that vocalize more frequently, at higher amplitudes and hold larger territories will be better‐suited to sampling‐based acoustic methods.

Uncovering the rich amphibian fauna of two semideciduous forest fragments in southwestern Bahia, Brazil.

Fauna inventories reduce biodiversity knowledge gaps by providing comprehensive data on species distribution, richness, and abundance. Furthermore, they identify undocumented species and enhance understanding of ecosystem dynamics and conservation needs. The richness and abundance of amphibian species were studied in two Semideciduous Seasonal Forest areas in the municipalities of Potiraguá (Serra Azul) and Itarantim (Serra do Mandim) in southwestern Bahia, Brazil. Active visual and acoustic surveys were conducted in 24 forest interior transects, two stream transects, and two permanent ponds investigated in the study area. Opportunistic encounters during team movements were also recorded. The richness was 46 amphibian species distributed in 14 families and 26 genera. Approximately half of the species were shared between the two areas, while 11 species were exclusive to Serra Azul and another nine were found only in Serra do Mandim. Cluster analysis for 42 locations in Atlantic Forest, Caatinga, and Cerrado, in a presence/absence matrix with 216 species, revealed that the composition of the amphibians found in Serra do Mandim and Serra Azul is similar to other sampled locations in the northeastern region of Minas Gerais, close to the study site, which are considered transitional between the Atlantic Forest and the Caatinga. Our results demonstrate that the remaining forest fragments in the region, although small and isolated, still sustain a high richness of amphibians with species restricted to the Atlantic Forest and Bahia, such as Bahiusbilineatus, Ololygonstrigilata, Aplastodiscusweygoldti and Vitreoranaeurygnatha, and others considered typical of the Caatinga, such as Leptodactylustroglodytes and Physalaemuscicada. Additionally, we sampled potential new species, filled occurrence gaps, and expanded the geographical range of Pseudisfusca.

Resource abundance of cobalt-rich ferromanganese crusts in the KC-8 seamount, West Pacific

We have estimated the resource potential of cobalt-rich ferromanganese crusts (CFCs) on the summit area of the KC-8 seamount in the West Pacific, based on the acoustic backscatter intensity (ABI), ROV video footage, and CFC thickness measurements. To estimate the spatial distribution of CFC across 13 equally divided blocks within a 360 km2 area, shipboard and deep-tow ABIs were compared with visual data. The presence of CFCs is evident in the areas where ABI is higher than average, validating the use of ABI data to delineate the exposure of CFCs. With high accuracy in distinguishing between CFCs and sediment-dominant areas, the distribution area of CFCs was precisely calculated. The variation in CFC thickness across the KC-8 seamount summit was measured through CFC samples retrieved using a CFC corer. CFC thickness is highly variable even between adjacent sites, but it shows a roughly increasing trend from south to northwest. Based on the CFC distribution area associated with thickness, we calculated a CFC resource abundance. Of the estimation, 82% have remained on the gentle slope (<10°) areas, which can be accessible for future mining. Overall, our study suggests that the combination of an acoustic survey with reliable thickness information is highly effective in estimating CFC abundance.

Double tombolo formation by regressive barrier widening and landside submergence: The case of Orbetello, Italy

The double tombolo of Orbetello, in Italy, has formed during the Holocene around an ancient central tombolo. Earlier models consider that its sand barriers formed as sand spits that stretched from the mainland to a coastal island before enlarging seawards. This evolution, however, remains speculative. In order to test these models, we conducted the first study of a double tombolo that combines coring of its sand barriers and comprehensive imaging of its internal structure using sub-bottom acoustic surveys offshore and in the back-barrier. Sediment ages were constrained by 14C, luminescence, and U/Th dating. Acoustic images below the lagoon show that the barriers are in fact broad regressive strandplains that initiated on the flanks of the preexisting central isthmus when sea level was −7 ± 1 m lower than today. The strandplains then rose upwards and outwards, tracking sea level rise over the past 7 kyr. The oldest and lowest parts of the strandplains were flooded into the shallow intervening lagoon. The central isthmus is composed of regressive sand barriers accreted around a MIS 5.5 core during subsequent stages MIS 5.3 and MIS 5.1. The emplacement of the isthmus interrupted longshore drift between the mainland and the coastal island, converting the flanks of the initial tombolo into terminal sinks in which sand accretion accelerated, spurring early and rapid regression during the Holocene. A review of the environmental parameters conducive to double tombolo formation suggests that double tombolos may represent a frequent, albeit short-lived stage during the enlargement of single tombolos.

Noise sensors - Part 1: Usage for the redesign of neighbourhoods

An interdisciplinary research project at the Stuttgart University of Applied Sciences with participation of the departments of urban planning, surveying and geoinformatics, business psychology and acoustics, present alternative urban scenarios. Different aspects for the redesign of the district, especially measures to reduce the individual motorised transport, were investigated. Virtual reality and augmented reality experiments are used in public spaces, to show redesign possibilities. Surveys of people, who had the experience of the future scenarios via the AR application and VR application, were carried out. Additionally, acoustical surveys and measurements in this research project were performed using so called noise sensors. These sensors based on MEMS microphones were developed for a simple and cost-effective measurement of external noise in a citizen sciences project. The measurement results of the noise sensors are saved online and can be accessed on the homepage "Sensor.Community". One of the noise sensors was used in the project area over a longer period. Measurement values were generated in third octave bands at intervals of 5 s and are available for further evaluations, e.g. for the calculation of indoor noise levels. The paper presents the research project and reports about the application of the noise sensor.

Room acoustic survey of open and enclosed learning spaces in Finland

Use of open learning spaces for education has increased in schools while enclosed learning spaces are still used in most schools in overall. There is some debate that these two learning space types might differ in acoustic perceptions. If they do, room acoustic quality might be one explaining factor. Therefore, our purpose was to determine, whether these learning space types differ in room acoustic properties. We studied 10 schools with mostly enclosed and another 10 schools with open or flexible learning spaces in Finland. Altogether 73 learning spaces were investigated among the 20 schools. Measurements concerned reverberation time, Speech Transmission Index, and background noise level. Most of enclosed learning spaces (63%) met the new requirements of Finnish building regulations for enclosed learning spaces. Opposite to that, most of open learning spaces (91%) did not meet the regulations for open learning spaces. The results can be used in the root cause analysis of a teacher survey conducted in the same 20 schools. Teacher survey will be reported in another study. Parallel analysis of objective and subjective results is necessary to judge whether the current regulations are justified.

Underwater sound produced by operational floating wind turbines

Deployment of offshore wind turbines is growing rapidly. Conventional "fixed bottom" wind turbines are limited to water depths of ~60 m, so deployment of offshore turbines to greater water depths requires floating systems. Both fixed bottom and floating turbines produce operational noise that impacts the marine environment. While the operational noises from fixed bottom turbines are relatively well understood, floating turbines are comparatively novel technologies and there is uncertainty as to the noise they will produce and its impact on the marine environment. Results from acoustic surveys of two floating wind farms off the Scottish Coast are presented; Kincardine wind farm which uses semi-submersible floating systems; and Hywind which uses a floating spar structure. The acoustic signature of each consists of continuous tonal noise related to drivetrain vibration and transient broadband events related to the mooring systems. A machine learning algorithm was used to discriminate between drivetrain noise and mooring noise. Sound propagation modelling was used to determine the source levels for turbines at each wind farm allowing a comparison of the noise signature of different floating structures.

Acoustic study of urban bat diversity in Veliko Tarnovo, Bulgaria

Urbanisation presents both challenges and opportunities for bat populations. Understanding the composition and distribution of urban bat species is the first step toward their effective conservation. However, comprehensive studies on urban bat diversity remain scarce in Bulgaria. To address this gap, we conducted a year-long acoustic survey on five different habitats in the urbanised territory of Veliko Tarnovo. Our study identified the presence of eight bat species and other distinct acoustic groups within the urban environment. Bats were found to utilise various habitats across the urban landscape. Although the activity was highest during May and September, bats remained active all year round, including the winter. Our study provides insights into synanthropic bats’ seasonal and microhabitat-dependent use of urban areas. These findings will establish a baseline for future research focusing on habitat preferences, population dynamics, and interactions with urbanisation. Such research is essential for the effective management and conservation of bat populations in urban environments.

Concurrent physical and acoustical observations of the upper-ocean near Atlantis II seamount using Wave Gliders

The rapid evolution of the physical properties of the upper ocean expected in regions with strong submesoscale features can lead to complex acoustic propagation effects. In spring 2023, an autonomous surface vehicle (LRI Wave Glider) was outfitted with a suite of oceanography and acoustic equipment and deployed in the Gulf Stream in a region located over the New England Seamounts, allowing an opportunity to study how the physical variability can affect the speed of sound and ambient soundscape. In August 2024, three more Wave Gliders were deployed in the same area. The vehicles, using GPS and time-synchronized equipment, were able to collect ambient acoustic data on a four-element hydrophone array, as well as local physical properties (e.g. CTD data, wind speed, and ADCP current data) that could affect the acoustic recordings during long term missions above and around the Atlantis II seamount. Two low frequency sources of opportunity were also able to be recorded over long distances, with noise level varying with vehicle position, allowing an understanding of acoustic propagation paths in this area. These long-term measurements demonstrate the unique capability of an autonomous surface vehicle for making wide-range acoustic surveys.

Importance of Manually Vetting Acoustic Bat Call Files: A Case Study for Northern Long-Eared Bats

Abstract Definitively identifying bats based on their acoustic calls is difficult and sometimes impossible. This is particularly true for Myotis species that can make similar calls, which could lead to false positive detections. This is problematic for conducting species presence or probable absence surveys using acoustic detection. Manual vetting of calls to reduce identification error by the automated programs is an option but not a requirement to survey for species listed as threatened or endangered pursuant to the Endangered Species Act. We conducted simultaneous mist net and acoustic surveys for bats in areas of Edgecombe and Johnston counties in eastern North Carolina where there are capture records of a common Myotis species, the southeastern myotis Myotis austroriparius, but not for the federally endangered northern long-eared bat Myotis septentrionalis. We caught southeastern myotis at six of the 12 sites surveyed. Although automated acoustics software produced a Maximum Likelihood Estimation value for probable presence of northern long-eared bats at three of the 12 sites surveyed, we did not catch any individuals or confirm the species acoustically through manual vetting. If we had used automated software alone without manual vetting, we would have incorrectly presumed presence of an endangered species at 25% of our sites. Therefore, manual vetting is highly recommended for northern long-eared bat acoustic surveys where southeastern myotis co-occur.

Paired comparisons with quiet surface drones show evidence of fish behavioral response to motorized vessels during acoustic surveys in Lake Superior

Acoustic surveys are important for fish stock assessments, but fish responses to survey vessels can bias acoustic estimates. We leveraged quiet uncrewed surface vessels (USVs) to characterize potential bias in acoustic surveys. Five conventional motorized ships overtook USVs from astern over 2 km transects at night in Lake Superior in 2022. We examined the difference in acoustic backscatter, average target depth, and average target strength (TS) between USV and motorized vessels. Although sound level measurements from the motorized vessels sometimes exceeded recommendations for scientific vessels, we did not detect differences in acoustic measures among survey vessels. However, the USVs recorded 2 dB higher acoustic backscatter and TS than motorized vessels, leading to ∼15% higher fish densities with drones when using in situ TS and echo integration. Differences in fish density would increase to 30%–60% if a standard TS value was applied. Target depth did not differ between USVs and motorized ships. These results are consistent with a change in orientation but not depth of insonified fish and limited horizontal avoidance of motorized survey vessels.

Fourier-transform near-infrared spectroscopy first application to age determination in European fish species: the case of the Atlantic horse mackerel from the central Mediterranean Sea

Fourier-transform near-infrared spectroscopy (FT-NIRS) has recently been used to reduce the processing time for estimates of annual age in several fish species. The present study represents the first application of this technique to marine organisms from the European waters. Atlantic horse mackerel (Trachurus trachurus) from the central Mediterranean Sea was selected for its ecological role, its socioeconomic value, and because its age is regularly estimated by otolith reading under a stereomicroscope for stock assessment purposes. Absorption spectra of the whole otoliths were acquired by FT-NIRS across a multiyear dataset, obtained during acoustic surveys carried out in different regions of the central Mediterranean Sea. The acquired spectra were processed to optimize calibration models to predict age. The best linear models obtained by the optimizing procedure predicted age successfully with a coefficient of determination of 0.95–0.96, mean squared error of 0.5 years, and bias <0.03 years. Although regional calibration models were also obtained separately, the models with all regions combined appeared much more robust and encompassing the whole age range, suggesting its usefulness for the entire spatial distribution range considered in the preset study. The use of FT-NIRS allowed to successfully predict age for horse mackerel between the ages 1 and 14, with similar or better precision (and bias) of the traditional methods, also increasing the standardization by repeatability of age assignments. The preliminary results obtained by this study encourage further effort to fine-tune the calibration model for new species, in order to apply a precise, rapid, cost-effective method for stock assessment purposes of Mediterranean fish resources.

A Three–Year Comparison of Fluctuations in the Occurrence of the Giant Jellyfish (Nemopilema nomurai)

In this study, acoustic, sighting, trawl, and marine environmental surveys were used to determine the vertical distribution and density of giant jellyfish that have been observed in Korean waters over the past 3 years. From 2020 to 2022, annual surveys were conducted in May and July in the East China Sea and waters adjacent to South Korea. The acoustic data were processed by identifying and eliminating all signals considered as noise while excluding those suspected to be jellyfish signals. Subsequently, a single target detection method was employed. Giant jellyfish are distributed mostly in the middle and low layers. In May 2021, the average population density of giant jellyfish was recorded as 11.6 (ind./ha), which was the highest density. In July 2022, this value decreased to 1.7 (ind./ha), marking the lowest density. The sighting survey, which allows for the identification of jellyfish distributed in the surface layer, exhibited a difference of approximately 0.13 times compared to the acoustic survey conducted in the middle and low layers in 2020. In 2021 and 2022, this difference was approximately 0.11 times and 0.24 times, respectively. The average of this difference was 0.16 times or greater.